Review the general role of neurotransmitters and neuromodulators.

Neural communication is the basis for all brain functions and is essential for understanding how the brain processes information. It involves a complex network of neurons, which are the basic units of the brain, communicating with each other through electrical and chemical signals.

Each neuron receives signals through its dendrites, processes these signals in its cell body, and then sends out a response via its axon. This axon can connect to the dendrites or cell bodies of other neurons, creating a vast network of interconnected cells. The point where one neuron connects to another is called a synapse, and it is here that the chemical part of neural communication occurs, facilitated by neurotransmitters.

Synaptic transmission is the process by which neurons send chemical signals to communicate with each other. This occurs at the synapse, where the axon terminal of one neuron is in close proximity to the dendrite or cell body of another neuron.

When an electrical signal, known as an action potential, travels down the axon to the axon terminal, it triggers the release of neurotransmitters from vesicles into the synaptic cleft – the space between the neurons. These neurotransmitters then bind to receptors on the post-synaptic neuron, causing changes that result in either an excitatory or inhibitory response, depending on the type of receptors and neurotransmitters involved.

Neurotransmitters serve as the chemical messengers that facilitate synaptic transmission. They are synthesized in the neuron and stored in vesicles. Upon the arrival of an action potential, they are released into the synaptic cleft and travel across this gap to bind with specific receptors on the surface of the post-synaptic neuron.

The binding of neurotransmitters to these receptors causes a change in the post-synaptic neuron, such as the opening or closing of ion channels, leading to a depolarization or hyperpolarization of the neuron. This is how neurotransmitters can influence whether a neuron will generate a new action potential.

Neuromodulators differ from neurotransmitters in that their role is not to directly transmit signals, but rather to influence the strength and duration of the signal transmission. They do this by altering the response of the neurons to neurotransmitters.

For instance, a neuromodulator might increase the sensitivity of a neuron to a particular neurotransmitter, thereby amplifying its effects, or it might decrease the sensitivity, diminishing the neurotransmitter's effects. This modulation happens through various mechanisms, such as changing the number of receptors, altering neurotransmitter breakdown, or affecting neurotransmitter reuptake. The influence of neuromodulators tends to be broader and longer-lasting compared to the more localized and short-term effects of neurotransmitters.